The present invention generally relates to the hoisting apparatuses and more particularly refers to an elongated boom automatically balanced by counterweight and suspended on the crane lift line for the use in locating loads under various types of roofs, or for increasing the crane-serving areas.
From prior art (U.S. Pat. No. 3,675,961 to Wheeler issued July 11, l972; U.S. Pat. No. 3,762,755 to Saether issued Oct. 2, 1973), it is known that only electro-automatical systems were used for the automatical balancing elongated boom with the load. This system utilizes several electrical switches, electrical motor and power supply arrangements which are all subjects to random failure and therefore could not meet existing high standards of safety for cargolifting devices.
The first patented hoisting device which may satisfy the standards of safety, utilizes purely mechanical automatical system for balancing elongated boom with counterweight, is granted in my name (U.S. Pat. No. 4,017,109 issued Apr. 12, 1977). The reason why this device will satisfy the high standards of safety is that it consists of only mechanical elements and the high reliability of each of them is proved by several types of existing hoisting devices utilizing similar elements.
Objectives of this invention are improvements of patented HOISTING DEVICE FOR A CRANE, U.S. Pat. No. 4,017,109.
The main ivention consists of an elongated boom with a moveable counterweight which automatically balances the boom when it picks up the load, relatively to the fulcrum axis to which crane lift line is attached.
In the unloaded condition the center of gravity of all system incuding the counterweight is located under the fulcrum axis and on the vertical continuation of the crane lift line. At the moment when a crane starts to lift the load first moves up the fulcrum axis, to which the crane lift line is connected, thus inclining the boom around the fulcrum axis because the load at this moment is not balanced. During this inclination the angle between the crane lift line, which under gravity forces is permanently in vertical position, and the boom is changing. Due to the purely mechanical system this angular alteration transfers to horizontal movement of counterweight off its central location along the guiding trucks on the boom in direction opposite to the load location. At the moment when counterweight moves from its central position on such a distance that it balances the load on opposite side of the boom, the inclination of the boom stops and all parts of the boom including the load start to lift up simultaneously with the crane lift line.
Improvements of this invention are as follows:
The first improvement relates to the guides for the counterweight. Improved railguides for the counterweight are so curved that the gravity force of the counterweight is all time normal to the curve while the counterweight moves along the curved part of the boom proportionally to the angle of boom inclination. This feature allows to increase angle of the boom inclination, it reduces considerably acting forces and as a consequence reduces the size of the mechanism for moving counterweight comparatively to straight quides which are on the patented device.
The second improvement which is used in a second embodiment relates to the mechanism transferring the boom inclination in the reciprocating motion of the counterweight. Proposed is a system of levers which consists of an intermediate lever and a driving lever. The driving lever is connected through an articulated joint on its upper part to a bearer which is an integrated part of a pivotal part of the boom. Through the intermediate lever the driving lever receives angular movement proportionally to the angular inclination of the boom. Proportional angular movement of the lower end of the driving lever, through the sliding frog and elongated opening in the middle of the counterweight carriage, transfers to a proportional movement of the counterweight along the curved guides.
This improvement simplifies considerably the mentioned mechanism comparative to a patented device, eliminating gear and chain transmission by substituting them with simple levers. The reliability of the levers is higher, manufacturing cost is less and they practically do not require any maintenance.